Conventional scanner designs use a contact image sensor datumed to the underside of the platen/continuous velocity transport (CVT) glass via only two buttons or bumps. As the image sensor moves across the transition between the CVT and the platen, a disturbance in the imaging is observed. This problem is also observed in scanning systems using Full Width Array (FWA) or folded Charged Coupled Device (CCD) optics designs.
FIG. 1 illustrates a conventional scanner system 10 that uses only two buttons at the end of the optics carriage and therefore experiences turbulent motion during the transition between the CVT and platen, which results in unwanted motion disturbances, which in turn affect image quality. The system shows a continuous velocity transport (CVT) glass portion 12, a continuous velocity transport ramp 14 comprising a calibration strip 16, and a platen glass portion 18. The system further comprises a contact image sensor (CIS) module 20 that includes two buttons, 22 and 24, which support the continuous velocity transport, continuous velocity transport ramp, and platen as the scanner moves during scanning.
A conventional continuous velocity transport ramp picks paper up off the continuous velocity transport glass and guides it into a document handler. To prevent stub points, the conventional continuous velocity transport ramp is arranged to extend below the continuous velocity transport glass, as such the CVT glass must be separate from the platen glass. It is not possible to get a perfectly flat area from the CVT glass to the underside of the ramp and to the platen glass due to glass and molding tolerances. Therefore, there is a difference in height as the CIS module transitions from the continuous velocity transport glass portion across the ramp area to the platen glass. In the conventional configuration, the continuous velocity transport ramp molding (the bottom of the continuous velocity transport ramp between the continuous velocity transport glass and platen glass portions) sits slightly below the continuous velocity transport glass and platen glass heights, and as the buttons 22, 24 pass under this area, the imaging point and height is disturbed. This gives rise to a disturbance in the sensed brightness of the calibration strip as illustrated in FIGS. 2-3.
FIG. 2 shows an image 40 of a calibration strip reading where motion disturbance has occurred, such as is caused by jitter cause by the transition of the unevenly arranged continuous velocity transport ramp over a button. That is, the bottom surface of the continuous velocity transport ramp, being lower than the bottom surfaces of the continuous velocity transport glass and the platen glass, introduces a disturbance during the transition of the CIS module buttons as they pass across the continuous velocity transport ramp bottom surface. This, in turn, causes the distance from the imaged surface to the calibration strip to be inconsistent, which results in the gray value measured from the calibration strip to be inconsistent as well, as illustrated by the lines 42. A similar disturbance can occur in the platen area.
FIG. 3 illustrates a graph 50 plotting positional disturbance (in microns) on the y-axis against slow scan distance (in pixels) on the x-axis. As can be seen, there two peaks 52 that correspond to the lies 42 of FIG. 2. The two peaks 52 represent disturbances cause by the transition of the lower edge of the continuous velocity transport ramp as it passes over a button. The measured gray values are affected by the inconsistency in the distance of the scanned page from the calibration strip during the transition of the continuous velocity transport ramp lower surface over the buttons(s).
FIG. 4 shows a graph 60 of a motion quality effect 62 that occurs at the beginning of the platen scan when the conventional image module is still vibrating from the ramp disturbance. Positional disturbance (in microns) is shown on the y-axis and slow scan distance (in pixels) is shown on the x-axis.
There is a need in the art for a carriage module and CVT-platen arrangement that facilitates mitigating motion disturbances during CVT-to-platen transition during scanner motion, while overcoming the aforementioned deficiencies.